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Basic DBMS ppt

2.
DATABASE : A collection of data is referred to as
database.
e.g. 1. record of students stored in files
2. information stored over internet
DATABASE MANAGEMENT SYSTEM: It is basically a
computer based record keeping system (program).
e.g. MySQL
Microsoft Access
FileMaker
FoxPro

4.
Various levels of database implementation (concept of abstraction)
1.INTERNAL LEVEL (PHYSICAL LEVEL):
It describes how data are actually stored on the storage
medium.
It is closest to database programmer.
Lowest level of database abstraction.
2. CONCEPTUAL LEVEL:
It describes what data are actually stored in database.
It is closest to the database manager.
It is an intermediate level of database abstraction.
•EXTERNAL LEVEL (VIEW LEVEL):
It describes the way in which the data are viewed by individual
user.
It is the level closest to the users.

9.
Relational Data Model
The relational model was put forward by E.F. Codd of the IBM.
It is considered as a very important concept in DBMS.
Some basic terminologies
Relation : A relation is a table i.e. data is arranged in rows and columns.
Tuple : The rows of tables are generally referred to as tuples.
Attributes : The columns of tables are generally referred to as attributes.
Degree : The number of attributes in a relation determine the degree of
the relation.
Cardinality : The number of tuples in a relation is called the cardinality of
the relation.

10.
Views
A view is a (virtual) table that does not really exist in its own right but is
instead derived from one or more underlying base tables.
It is an excellent way to give people access to some but not all
information (data abstraction).
Database Keys are used to establish and identify relations between
tables.
Primary key: It is a set of one or more attributes that can uniquely
identify the tuples within the relation.
Candidate key : All attribute combinations inside a relation that can
serve as a primary key are candidate keys.
Alternate key: A candidate key that is not the primary key is called the
alternate key.
Foreign key : A foreign key is a non key attribute whose value is derived
from the primary key of another table.